THE VIRUS OF HYDROPHOBIA 617 



with the argument that the smaller internal formations may be 

 the infective agent in its essential form, and a modification of 

 this view is that the Negri body is a cellular reaction against 

 an invasion with these ultimate forms (see p. 622). The whole 

 question must be looked upon as sub judice. 



There is no doubt that between rabies and the bacterial 

 diseases we have studied there are at every point analogies, the 

 most striking being the protective inoculation methods, the dis- 

 covery of which constitutes the great work of Pasteur ; and every- 

 thing points to a micro-organism being the cause. The organism, 

 whatever it is, is, in its infective form, probably very small, as it 

 can pass through the coarser Berkefeld niters, and also occasion- 

 ally through the coarser Chamberland candles. Evidence that it 

 is the organism itself which passes through, is found in the fact 

 that when an animal dies from infection with the filtrate, a 

 small portion of its central nervous system will originate the 

 disease in a fresh animal. Judging from our knowledge of 

 similar diseases, we would strongly suspect that it is actually 

 present in a living condition in the central nervous system, the 

 saliva, etc., which yield what we have called the hydrophobic 

 virus, for by no mere toxin could the disease be transmitted 

 through a series of animals, as we shall presently see can be 

 done. A toxin may, however, be concerned in the production 

 of the pathogenic effects. Remlinger found that death with 

 paralytic symptoms followed the injection of filtered virus, but 

 that the nervous system of the dead animals sometimes did not 

 reproduce rabies. He explains this occurrence by supposing that 

 the filtrate contained a toxin but not the actual infective agent. 

 The resistance of the virus to external agents varies. Thus a 

 nervous system containing it is virulent till destroyed by putre- 

 faction ; it can resist the prolonged application of a temperature 

 of from - 10 to - 20 C., but, on the other hand, it is rendered 

 non-virulent by one hour's exposure at 50 C. Again, its 

 potency probably varies in nature according to the source. 

 Thus, while the death-rate among persons bitten by mad dogs is 

 about 16 per cent., the corresponding death-rate after the bites 

 of wolves is 80 per cent. Here, however, it must be kept in 

 view that, as the wolf is naturally the more savage animal, the 

 number and extent of the bites, i.e., the number of channels of 

 entrance of the virus into the body and the total dose, are 

 greater than in the case of persons bitten by dogs. As we shall 

 see, alterations in the potency of the virus can certainly be 

 effected by artificial means, such as drying, heating, and applying 

 chemical agents. 



